A federal judge yesterday approved a consent decree removing the broadcasting industry's self-imposed limits on the length, placement and frequency of television commercials.

The decree approved by U.S. District Judge Harold H. Greene is not expected to produce an explosion of new commercial interruptions for television viewers, however, according to network and local television officials reached yesterday. They said they planned to continue following the limits set by the National Association of Broadcasters, which were canceled by the consent decree.

"It's not in our best interest to increase the advertising time," said Thomas B. Cookerly, general manager of Channel 7 (WJLA, ABC) here. "We're generally operating at a lower load than the NAB allowed" for television commercials. "I know we're not going to increase it" now that the NAB limits have been lifted, Cookerly said.

"Today's decision will have no effect on NBC's advertising acceptance policies, which are set by NBC's own broadcast standards codes," said a National Broadcasting Co. official.

Judge Greene's approval of the decree, which was largely fashioned by NAB lawyers with the consent of Justice Department attorneys, supersedes his ruling March 3, when he found the NAB guilty of antitrust violations.

For example, Greene said then that the NAB's rule forbidding more than one product promotion in any 60-second commercial was "an artificial device to enhance the demand for commercial time."

The NAB appealed Greene's decision. While the matter was pending in the U.S. Court of Appeals, however, the broadcasters' group voluntarily stopped enforcing its self-styled regulations governing television commercials. The voluntary plan was submitted to Greene who, by accepting it, absolved the NAB of antitrust guilt and spared the government the expense of a continuing court fight.

However, NAB officials were less than sanguine about the outcome.

"This is a sad day for the American public," said NAB President Edward O. Fritts. "Pure and simple, today's action means that the government does not want television broadcasters to attempt to govern themselves by voluntarily limiting the amount of advertising broadcast into the public's homes," Fritts said yesterday.

He added: "Broadcasting as a guest in the home is unlike any other business in the nation. Thus, television broadcasters feel a unique responsibility to maintain a balance of programming and advertising. We are dismayed" by the end of the case, which began June 14, 1979, with a Justice Department complaint.

Under the decree, the NAB "shall immediately cancel" its code governing "the quantity, length or placement of non-program material appearing on broadcast television" and "the number of products or services presented within a single non-program announcement on broadcast television."

The major restrictions in the code included limits on the minutes each television station may devote hourly to commercials, on the number of commercials each hour, and on the number of consecutive promotions within each commercial interruption.